How do I submit an assignment on behalf of a student as an instructor?
If enabled by your institution, you can submit an assignment on behalf of a student in the Gradebook.
Notes:
- A File Upload submission type must be allowed to submit an assignment on behalf of a student.
- If you are unable to submit on behalf of a student, your institution has not enabled this permission. Please contact your Canvas admin.
Open Grades

Open Grade Detail Tray

Locate the student name and assignment. Click the Gradebook cell [1] and click the Grade Detail Tray icon [2].
Submit for Student

To submit for a student, click the Submit for Student link.
Upload File

To upload a file from your computer, drag and drop a file [1], or browse your computer files by clicking the Choose a file to upload link [2]. To submit the file, click the Submit button [3].
View Submission Details

View submission details in the Grade Detail Tray. You can also view the uploaded file uploaded in Speedgrader.
Note: Students and Observers can see the submission details when they view the assignment.
[Content retrieved from https://community.canvaslms.com/t5/Instructor-Guide/How-do-I-submit-an-assignment-on-behalf-of-a-student-as-an/ta-p/560948]